Metallic Thin Film Type Magnetic Recording Medium and Method of Manufacturing Thereof

ABSTRACT

A method of manufacturing a metallic thin film type magnetic recording medium is provided. The method comprises the steps of arranging an initial substance of said recording medium in opposition to a plasma discharge electrode, said initial substance comprising a non-magnetic support base, a metallic layer capable of functioning as a metallic electrode formed on said non-magnetic support base and a metallic magnetic layer formed on said metallic layer, and forming a protection film on a surface of said initial substance of said recording medium by way of generating plasma discharge while feeding raw material gas between said metallic layer/said metallic magnetic layer and said plasma discharge electrode.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/183227 filed Jun. 27, 2002, which is incorporated herein by referenceto the extent permitted by law. This application claims the benefit ofpriority to Japanese Priority Document JP 2001-199370, filed in theJapanese Patent Office on Jun. 29, 2001, which also is incorporatedherein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a so-called metallic thin film typemagnetic recording medium comprising metallic magnetic thin film formedon a non-magnetic support base and a method of manufacturing it. Moreparticularly, the present invention relates to a metallic thin film typemagnetic recording medium available for a durable video tape with alonger recording time or a tape for high density magnetic recording,which may be used as a large capacity tape streamer. The presentinvention also relates to a method of manufacturing such a magneticrecording medium.

2. Description of the Related Art

Conventionally, such a so-called coating type magnetic recording mediumis widely known as a magnetic recording tape for recording audio signaland video signal. The coating type magnetic recording medium ismanufactured by coating and drying of magnetic paint on non-magneticsupporting base. The magnetic paint may be produced by way of dispersingmagnetic powder such as magnetic oxide powder or magnetic alloy powderin a variety of bonding agents such as copolymer of vinyl chloride andvinyl acetate, polyester resin, polyurethane resin, or urethane resin,for example.

Along with growing demand for higher density recording in recent years,so-called magnetic thin film type magnetic recording medium has beenintroduced. This type of magnetic recording medium comprises a magneticlayer directly formed on a non-magnetic supporting base or via anextremely thin adhesive layer. The magnetic layer is formed usingmetallic magnetic material such as Co—Ni alloy, Co—Cr alloy, or Co—O byapplying a variety of vacuum thin film forming techniques such as aplating method, vacuum vapor deposition method, sputtering method, orion plating method, or the like.

Because of distinguished coercivity, square ratio, and capability toform a magnetic layer into an extremely thin layer, the above metallicthin film type magnetic recording medium has a superior electromagneticconversion characteristics in short wave band and can significantlyminimizes demagnetization in the recording and loss of thickness duringa replay operation as well. Further, unlike the coating type magneticrecording medium, inasmuch as no binder comprising non-magnetic materialis present in the magnetic layer, it is possible to enhance density offerromagnetic metallic particles to be filled therein, thus providingvarious advantages.

Further, in order to improve electromagnetic conversion characteristicsand generate larger output, such a method of obliquely forming themagnetic layer via so-called diagonal vapor deposition method hasalready been in practical use.

Typically, in the above cited metallic thin film type magnetic recordingmedium, in order to improve durability and running characteristics,either a protection layer is formed on the magnetic layer or a backlayer is formed on the opposite side surface from the surface on whichthe magnetic layer is formed.

Further, in the metallic thin film type magnetic recording medium, inorder to minimize spacing loss in correspondence with the higher densityrecording, the surface of this magnetic recording medium has beensmoothened furthermore.

Nevertheless, after further smoothening the surface of the magneticlayer, an area in contact with a magnetic head expands. The expansioncauses friction force to be intensified and shearing force in themagnetic layer to be risen. In order to protect the magnetic layer fromsuch severe frictional sliding condition, a protection film may also beformed over the magnetic layer.

It is known that the protection film can be formed with a carbon film, aquartz (SiO₂) film, or a zirconia (ZrO₂) film, for example. These filmshave already been applied to a hard disc. In recent years, among avariety of carbon films, a rigid carbon film (so-called a diamond-likecarbon film) formed with diamond structure has widely been utilized as adistinguished protection film. The protection film comprising rigidcarbon is formed by applying such a typical sputtering method or aplasma CVD (chemical vapor deposition) method.

In the case of applying the sputtering method, initially, availing ofelectric field or magnetic field, sputtering gas comprising argon gas isionized and turned into plasma, and then the plasma is accelerated tohit against a target surface. Target atoms are sputtered out from thetarget surface to which the plasma particles are collided. The sputteredatoms are deposited on an object to be processed to form a sputter film.However, in the case of forming the rigid carbon film via the sputteringprocess, it is found that a rate of forming the carbon film is generallyslow. Accordingly, this sputtering process is disadvantageous in view ofindustrial productivity.

On the other hand, in the case of applying the above plasma CVD method,initially, raw material gas for forming the film is subject to chemicalreaction thereby generating decomposition or synthesis of the rawmaterial gas by effect of energy of plasma generated by the electricfield. Resultant material generated from the chemical reaction is thendeposited on the processed object to form the CVD film. The plasma CVDmethod forms the CVD film much faster than the above sputtering method,and thus, the plasma CVD method is quite promising as an effective meansfor forming the rigid carbon protection film.

Referring to a plasma CVD processing apparatus shown in FIG. 2, a methodof forming a rigid carbon protection film using the plasma CVD method isdescribed below.

The plasma CVD processing apparatus shown in FIG. 2 comprises a vacuumchamber 11 including a cylindrical rotating support body 12 with groundpotential, a reaction tube 13 disposed by way of facing the rotatingsupport body 12, and a discharge electrode 14 fitted inside of thereaction tube 13. An end 15 of the reaction tube 13 penetrates thebottom portion of the vacuum chamber 11 in order to introduce reactiongas for forming a rigid carbon film including vaporized aliphatichydrocarbons such as ethylene or such gas comprising aromatichydrocarbon vaporized from liquid material such as toluene for exampleinside of the reaction tube 13 via an end 15 of the reaction tube 13. Itis preferred to utilize the discharge electrode 14 that is capable ofeasily letting gas components through it and evenly generating electricfield. Accordingly, it is preferred to configure the discharge electrode14 with a mesh form for accommodating structural flexibility. Althoughcopper is cited as a typical material, any metal having a reasonablylarge electric conductivity may also be utilized, which includesstainless steel, brass, and gold, for example.

In the plasma CVD processing apparatus shown in FIG. 2, an object 16 tobe processed and formed with a CVD film is guided between a supply roll17 and a take-up roll 18 by a pair of guide rolls 19 in order that itcan continuously run itself along the surface of the above rotatingsupport body 12. When the object 16, which continuously running throughthe rolls, arrives at a location of the rotating support body 12corresponding to a position opposite from the discharge electrode 14,plasma is generated between metallic magnetic layer of the object 16 andthe discharge electrode 14 to cause reaction such as decomposition orsynthesis of raw material gas to be generated. As a result, decomposedor synthesized material generated via the above reaction is deposited insuccession to cause the CVD film consisting of such a rigid carbonprotection film. Simultaneously, current is grounded via the object 16and the rotating support body 12 having the ground potential.

As described above, by operating the above plasma CVD processingapparatus shown in FIG. 2, the raw material gas is decomposed by effectof plasma discharge between metallic component present in the object 16and the discharge electrode 14, whereby forming a rigid carbonprotection film.

SUMMARY OF THE INVENTION

In response to a demand for still higher density recording capability ofmagnetic recording media, in place of conventional induced type heads, amagneto-resistive effect type magnetic head (MR heads) has recently beenintroduced as a magnetic head usable for reading out recorded data.

The above MR head has characteristics capable of detecting minimalleakage flux from a magnetic recording medium with high sensitivity.Because of the characteristics, it is possible to eliminate noisecomponent by way of further thinning film of metallic magnetic layer toimprove surface recording density.

On the other hand, along with further thinning of the metallic magneticlayer, its specific resistance is increased to make it difficult toexecute stabilized discharge during the above plasma CVD processingapparatus.

Unless plasma discharge is stabilized, there are disadvantages such thatthe rate of forming the above rigid carbon protection film, which isformed through the plasma discharge, is decreased, and eventual qualityof the formed film can easily be deteriorated. Accordingly, the lowerthe film forming rate, the lower will be the number of magneticrecording medium produced per unit time, thus lowering productivity.

If it is merely intended to achieve stabilized discharge of plasma, theproblems may be solved by solely thickening a thickness of the metallicmagnetic layer. However, this may counteract the contemporary need tothin off the metallic magnetic layer to result in contradiction to theabove described recent trends in development of the metallic thin filmtype magnetic recording medium.

Accordingly, it is desirable to provide a metallic thin film typemagnetic recording medium capable of alleviating or solving the aboveproblems, forming a protection film at a preferable processing rate, andproperly decreasing overall thickness thereof. Further, it is desirableto provide a novel method of manufacturing the metallic thin film typemagnetic recording medium.

According to one embodiment of the present invention, there is provideda metallic thin film type magnetic recording medium comprising anon-magnetic support base, a metallic layer functioning as a metallicelectrode formed on the non-magnetic support base, and a protectionlayer formed on the metallic magnetic layer. Further, according toanother embodiment of the present invention, there is provided a methodof manufacturing the metallic thin film type magnetic recording medium.The method comprises the steps for disposing an initial substance of arecording medium comprising a non-magnetic support base, a metalliclayer functioning as a metallic electrode formed on the non-magneticsupport base, and a metallic magnetic layer formed on the metalliclayer, by way of facing a plasma discharging electrode, wherein themethod forms a protection film on a surface of the initial substance ofa recording medium by applying a vacuum thin film forming techniquewhich causes raw material gas to discharge itself while feeding the rawmaterial gas between the metallic layer/the metallic magnetic layer andthe plasma discharging electrode.

Embodiments of the present invention is described in detail below. Thepresent invention provides means to thin off the metallic thin film typemagnetic recording medium (this will merely be called a recording mediumin the following description) and improve its productivity. Further, thepresent invention provides means to form a protection film (to be formedon a recording medium) at a faster rate.

When the thinning off process of the metallic magnetic layerconstituting the main structural element of a recording medium isperformed as was done via the above referred conventional art, a speedof forming the protection film during the plasma CVD process, which isperformed after the thinning off process, may be lowered.

To prevent this, by way of preferably forming the metallic layercomprising non-magnetic metal between a metallic magnetic layer and anon-magnetic support base, the present invention provides technologiesfor simultaneously thinning off the recording medium and forming theprotection film at a faster rate.

In order to form the above metallic layer, it is preferred to use suchmetal or alloy having a specific resistance value lower than that of themetallic magnetic layer. The metallic magnetic layer may includealuminum, copper, tungsten, magnesium, molybdenum, silicon, and brass,respectively having a resisitvity equal or less than 420 Ω/inch².Although rather expensive from industrial viewpoint, gold or silver mayalso be used.

It is desirable that, by way of thinning a film thickness of the metallayer to a value thinner than the reduced amount of film thickness ofthe metallic magnetic layer, a film thickness of the recording medium isthinned off. Further, the thickness of the metallic layer is determinedso as to maintain sum of specific resistance values of the metalliclayer and the metallic magnetic layer within a predetermined range,thereby securing proper speed for forming the protection film as anessential function of metallic layer via the plasma CVD method.

A preferred film thickness of the metallic layer is dependent on avariety of conditions. Preferably, the film thickness may be set toequal or less than 100 nm, more preferably equal or less than 50 nm. Thesum of specific resistance values of the metallic layer and the metallicmagnetic layer is largely dependent on the thickness of the metallicmagnetic layer. Although a range of desired specific resistance valuesmay not generally be specified, when the metallic magnetic layer has50-100 nm of thickness, it is desirable that the preferable specificresistance value remains equal or less than 50×10⁻⁶ Ωm, and preferablyequal or less than 30×10⁻⁶ Ωm.

When forming the above protection film on the recording medium (initialsubstance of the recording medium) comprising the metallic layer havingthe above described characteristics by utilizing the above describedplasma CVD processing apparatus, because of the presence of the metalliclayer, the sum of specific resistance values of the metallic layer andthe metallic magnetic layer sharply decreases. This in turn stabilizesplasma discharge and makes it possible to hold the speed of forming arigid carbon protection film at a higher rate, and prevents the qualityof the formed film from being degraded. After thinning the thickness ofthe metallic layer to a value less than the reduced amount of the filmthickness of the metallic magnetic layer, overall thinning of therecording medium is achieved.

Further, by way of using material of a higher mechanical strength forcomposing the metallic layer, it is possible to maintain mechanicalstrength of the recording medium otherwise likely to cause mechanicalstrength to be lowered due to the thinning at such a degree equivalentto or more than that of a conventional recording medium having the filmthickness without having the thinning off process.

Individual elements other than the metallic layer are described below.Any of those known materials usable for a normal magnetic tape may alsobe used for composing the non-magnetic support base, which, for example,include the following polyester groups: polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polytetramethylenephthalate,poly-1,4-cyclohexanedimethylene phthalate, polyethylene 2,6-naphthalenecarboxylate, polyethylene-p-oxobenzoate, or the like. In particular,because of availability and ease of fabrications, PET and PEN aresuitable for use.

The above polyester group may comprise homo-polyester or copolyester.

Any of those ferromagnetic metals such as Fe, Co, Ni and any of thoseferromagnetic alloys cited below may be used for composing the metallicmagnetic layer to be formed on the metallic layer. The ferromagneticalloys may include Fe—Co, Co—O, Fe—Co—Ni, Fe—Cu, Co—Cu, Co—Au, Co—Pt,Mn—Bi, Mn—Al, Fe—Cr, Co—Cr, Ni—Cr, Fe—Co—Cr, Co—Ni—Cr, and Fe—Co—Ni—Cr.Further, the metallic magnetic layer may comprise a single layer ormultiple layers.

In order to form the metallic magnetic layer, a variety of vacuum thinfilm forming techniques may be utilized. For example, in the presentinvention, a vacuum vapor deposition method that thermally vaporizesmetallic magnetic material in vacuum and then deposits the vaporizedmetallic magnetic material on a metallic layer, an ion plating methodthat vaporizes metallic magnetic material in the discharge environment,and a so-called PVD technique including such a sputtering process toeject atoms from target surface by utilizing argon ion generated viaglow discharge took place in such ambient mainly comprising argon gas.

The protection film like a rigid carbon protection film for example isformed on the above referred metallic magnetic layer. Preferably, therigid carbon protection film comprises such a carbon film havingdiamond-like structure, in other words, it corresponds to the so-calleddiamond-like carbon film. Such carbon film consisting of graphitestructure or diamond-like structure is known. By way of measuring Ramanspectrum, individually derived peaks can be observed. In thediamond-like carbon film, at least a part of the carbon filmincorporates diamond-like structure. When measuring Raman spectrum,individual peaks derived from the diamond structure can be observed.Normally, such peaks derived from the diamond structure appear alongwith such peaks derived from graphite structure.

In order to form the protection layer, any of those known materialsconventionally used for composing a protection layer for protecting ametallic magnetic thin film may also be used. Not only carbon, but anyof those cited below may also be used, which, for example, include thefollowing: CrO₂, Al₂O₃, BN, oxidized Co, MgO, SiO₂, Si₃O₄, SiNx, SiC,SiNx—SiO₂, ZrO₂, TiO₂, TiC, MoS, or the like.

The above protection film may be formed by utilizing a known vacuum filmforming technique such as a plasma CVD method. The plasma CVD methoddecomposes carbon compound in plasma before forming thin film. Byutilizing the plasma CVD method, it is possible to stably form the rigidcarbon layer with a thickness equal or less than 10 nm, where the rigidcarbon is called diamond-like carbon which has distinguished wearresistant property, corrosion resistant property, surface coveringproperty, smooth surface configuration, and a high electric resistancevalue.

In this case, any of those known materials such as hydrocarbon group,ketone group and alcoholic group may be used for preparing carboncompound. In order to decompose the carbon compound in plasma, a certainbias voltage of high frequency may be utilized. While generating theplasma, in order to promote the decomposition of carbon compound, argongas or H₂ gas may be used.

In order to improve hardness and corrosion resistant property of thediamond-like carbon film, the carbon may remain in such a state that isbeing reacted with nitrogen or fluoride, and further, the diamond-likecarbon film may comprise a single layer or multiple layers. During thegeneration of plasma, the film may be formed in gaseous environmentincluding, in addition to the carbon compound, various gases such as N₂gas or CHF₃ gas or CH₂F₂ gas, or a proper mixture of these gases.

If the protection film is formed with an excessive thickness, a loss dueto spacing may increase. Conversely, if the protection film is formedtoo thin, the wear resistant property and the corrosion resistantproperty may be degraded. To prevent this, it is desirable that theprotection film be formed with 4-15 nm of thickness.

Further, whenever deemed necessary, it is preferable to form a backcoating layer on a surface opposite from the side in which the metallicmagnetic layer of the non-magnetic support base is formed, or form aground layer between the non-magnetic support base and the metallicmagnetic film in addition to the metallic layer, or form a lubricantlayer on the protection layer. In this case, such conventionally knownagents may also be used for composing non-magnetic pigments, resinbonding agent, or lubricating agent for preparing the back coatinglayer.

The recording medium according to the embodiments of the presentinvention is suitable for use as an MR head. Further, the recordingmedium may also be utilized for an induction type head.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe presently preferred exemplary embodiments of the invention taken inconjunction with the accompanying drawings, in which:

FIG. 1A presents a vertical sectional view for explanatory of apractical aspect for embodying a metallic thin film type magneticrecording medium related to the present invention;

FIG. 1B presents a vertical sectional view for explanatory of anotherpractical aspect of the metallic thin film type magnetic recordingmedium related to the present invention; and

FIG. 2 presents a vertical sectional view for explanatory of an exampleof a plasma CVD processing apparatus used for forming a rigid carbonprotection film by applying plasma CVD method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, a metallic thin film typemagnetic recording medium according to embodiments of the presentinvention is described below.

FIG. 1A presents a vertical sectional view of a metallic thin film typemagnetic recording medium in accordance with one embodiment of thepresent invention. FIG. 1B presents a vertical sectional view of ametallic thin film type magnetic recording medium in accordance withanother embodiment of the present invention.

In the metallic thin film type magnetic recording medium 100 shown inFIG. 1A, the upper surface of a non-magnetic support base 1 composed ofpolyester resin such as polyethylene terephthalate having 2-5 μm ofthickness is coated with a metallic layer 2 preferably having 20-100 nmof thickness by utilizing a vacuum vapor deposition process. It isdesirable that the upper surface of the metallic layer 2 be coated withlubricating agent and corrosion proof agent. Such a conventionallyavailable lubricating agent for application to a magnetic tape may alsobe utilized. The lubricating agent structurally based on fluorocarbon,alkylamine, or alkylester, is particularly suitable for use.

The metallic layer 2 is covered with a metallic magnetic layer 3 mainlycomposed of ferromagnetic metallic material. It is preferable that thesum of specific resistance values of the metallic layer 2 and themetallic magnetic layer 3 may remain equal or less than 50×10⁻⁶ Ωm.Further, the metallic magnetic layer 3 is covered with a protection film4 comprising rigid carbon protection film.

It is desirable that the above referred coating be applied to the bottomsurface of the non-magnetic support base 1. Further, by way of coatingthe back surface of the non-magnetic support base 1 with suchback-coating paint composed of polyurethane group substance, aback-coating layer 5 is formed.

In the recording medium 100 shown in FIG. 1A, the sum of specificresistance values of the metallic layer 2 and the metallic magneticlayer 3 is held below a predetermined value due to use of the metalliclayer 2 sandwiched between the non-magnetic support base 1 and themetallic magnetic layer 3. Accordingly, unlike such a conventionalrecording medium merely consisting of thinned thickness of the metallicmagnetic layer, the film forming rate is properly maintained above apredetermined value without causing the film forming rate to be loweredexcessively in the course of forming the protection film 4 by applyingvacuum film forming technique.

In the metallic thin film type magnetic recording medium 10A shown inFIG. 1B in accordance with another embodiment of the present invention,in addition to the metallic layer 2 shown in FIG. 1A, a reinforcinglayer 6 is disposed between the non-magnetic support base 1 and the backlayer 5. In the practical aspect shown in FIG. 1B, inasmuch as thereinforcing layer 6 promotes mechanical strength of the whole of themetallic thin film type magnetic recording medium 10A, it is possible tothin off the thickness of the non-magnetic support base 1 to be thinnerthan the that of a conventional support base without lowering overallmechanical strength thereof. Further, because of the presence of themetallic layer 2, it is possible to form the protection film 4 at such arate beyond the predetermined value.

EXAMPLES

Next, practical examples and comparative examples of the metallic thinfilm type magnetic recording medium in accordance with the presentinvention are described below. However, those practical examplesdescribed below do not restrict the scope of the present invention.

Examples 1-5 and Comparative Examples 1-4 Fabrication of the MetallicThin Film Magnetic Recording Medium

To constitute a non-magnetic support base for supporting the metallicthin film type magnetic recording medium shown in FIG. 1A, initially,such a polyethylene terephthalate film with 6 μm of thickness wasprepared.

While infusing oxygen during the vacuum vapor deposition process, byapplying the vapor depositing condition specified below, a metalliclayer was formed on a prepared non-magnetic support base.

Vapor depositing condition:

Metallic material: Al (Aluminum) 100% by weight

Vacuum condition during vapor deposition: 2.0×10⁻² Pa

Next, using the vapor depositing apparatus shown in FIG. 2, based on thevapor depositing condition specified below, a metallic magnetic layerwas formed by applying an oblique vapor depositing method.

Vapor depositing condition:

Metallic magnetic material: Co (Cobalt) 100% by weight

Incidental angle: 45°-90°

Process gas: Oxygen gas

Vacuum condition during vapor deposition: 2.0×10⁻² Pa

Next, based on the condition for forming a protection film specifiedbelow, a diamond-like carbon protection film was formed on a magneticlayer by applying plasma CVD method.

Protection film forming condition:

-   Process gas: Ethylene/argon mixed gas (Argon mixed rate 20% by    volume) 150 sccm

Reaction pressure: 30 Pa

Applied power source: DC 1.2 kV

Next, lubricating agent was applied onto a surface opposite from themagnetic layer formed surface. This lubricating agent was mainlycomposed of fluorocarbon, whose trade name was “Demtum”, a product ofDaikin Industrial Co., Ltd. This lubricating agent was denaturalized byapplying dimethyldecylamine corresponding to the tertiary amine and thensynthesized so as to form salt structure.

Next, the coated lubricating agent was superficially coated withpolyurethane back-coating paint by 0.5 μm of thickness by applyinggravure rolling method.

Next, the eventually produced metallic thin film type magnetic recordingmedium was cut into pieces. Then, the magnetic layer surface was coatedwith perfluoroether group lubricating agent. Finally, sampling magnetictapes were fabricated.

In the practical examples 1-5 (provided with a metallic layer and ametallic magnetic layer) and in the comparative examples 1-4 (solelyprovided with a metallic magnetic layer without having the metalliclayer), by way of adjusting film forming time under the above referredfilm forming conditions, a variety of samples with varied film thicknessof the metallic layer and the metallic magnetic layer were produced asshown in Table 1. Next, speed of forming film of the rigid carbonprotection film produced under an identical electric resistancecondition was measured per sample. In this case, electric resistance wasmeasured against 1 inch square surface area. Film thickness was measuredby utilizing sectional TEM method. The measured results per sample areshown in Table 1.

Measured results shown in Table 1 clearly indicate the following: In thecase of those samples without the metallic layer corresponding to thecomparative examples 1-4, when the film thickness was thinner than 50 nmas shown in the comparative examples 1 and 2, the film forming speed aredrastically decreased. It is presumed that, by way of thinning off thefilm thickness, electric resistance of the metallic magnetic layer haddecreased. On the other hand, relative to the increase of the filmthickness up to 50 nm as shown in comparative example 2, up to 100 nm asshown in comparative example 3, and up to 150 nm as shown in comparativeexample 4, the film forming speed was accelerated. Presumably, this isbecause of the decreased specific resistance of the metallic magneticlayer. Nevertheless, even though the film forming speed was accelerated,it was found that the comparative examples failed to thin off the filmthickness and also failed to down-size the whole of recording media.

In the case of the practical examples 1-5 individually having 50 nm ofconstant film thickness of the metallic magnetic layer and variedthickness of the metallic layer, relative to the increase of the filmthickness of the metallic layer up to 10 nm as shown in the practicalexample 1, up to 20 nm as shown in the practical example 2, up to 30 nmas shown in the practical example 3, up to 50 nm as shown in thepractical example 4, and up to 100 nm as shown in the practical example5, specific resistance values were lowered in turns to 31, 29.5, 27.2,13, and 9×10⁻⁶ Ωm. On the other hand, in such a manner inverselyproportional to the decreased specific resistance values, it was foundthat the speed of forming the protection film rose up to 320 nm, 370 nm,390 nm, 410 nm, and 430 nm per minute, respectively.

Comparison between the practical example 5, in which the metallicmagnetic layer had 50 nm of film thickness and the metallic layer had100 nm of film thickness, and the comparative example 3, which had 150nm of the metallic magnetic layer without incorporating the metalliclayer, clarified the following. That is, in the practical example 5, thespecific resistance value was as low as 9 and the film was formed atsuch a rate as fast as 430 nm per minute. In the comparative example 3,the specific resistance value was as high as 22.5 and the film wasformed at a rate of 392 nm per minute being considerably lower than thatof the practical example 5. By analyzing the above result, it was foundthat, in the case of such samples having identical film thickness, thosesamples based on the practical examples with the metallic layer formedthe film at such a rate much faster than the comparative examples.Accordingly, it is conceived that, in the case of the samples capable offorming film having an identical film forming speed, such samples withthe metallic layer can more easily achieve thinning of film than thesamples without the metallic layer

In view of productivity, it is desirable that the protection film(thickness of the protection film formed in an identical time duration)be formed as fast as possible. On the other hand, considering cost, itis also important to thin off the metallic layer as thin as possible.When considering such a need to restrain decrease of the speed forforming the protection film within 10% against a sufficient speed offorming film, if the metallic layer has a minimum of 20 nm of filmthickness, it is possible to restrain decrease of the protection filmforming speed within 10%. Further, it is preferable that the metalliclayer be provided with 20 nm of film thickness if possible. Value ofspecific resistance compatible with 20 nm of film thickness isrecommended to be 30×10⁻⁶ Ωm. TABLE 1 Thickness of Metallic Thickness ofSpecific Magnetic Metallic Resistance Protection Film Layer Layer (×10⁻⁶Ωm) Forming Speed Example 1 50 nm 10 nm 31 320 nm/min Example 2 50 nm 20nm 29.5 370 nm/min Example 3 50 nm 30 nm 27.2 390 nm/min Example 4 50 nm50 nm 13 410 nm/min Example 5 50 nm 100 nm  9 430 nm/min Comparative 30nm N/A 54 140 nm/min Example 1 Comparative 50 nm N/A 51 210 nm/minExample 2 Comparative 150 nm  N/A 22.5 392 nm/min Example 3 Comparative200 nm  N/A 20 420 nm/min Example 4

The present invention provides such a metallic thin film type magneticrecording medium which is formed with a metallic layer between anon-magnetic support base and a metallic magnetic layer. By virtue ofthe presence of this metallic layer, such problem causing speed offorming the protection film to be lowered due to the thinning of themetallic magnetic layer may be alleviated or solved, whereby making itpossible to provide such down-sized recording media at a higherproduction rate.

In other words, if a film thickness of the initial substance of arecording medium before formation of the protection film is thinner thana film thickness of a conventional corresponding initial substance of arecording medium, and if the sum of specific resistance values of themetallic layer and the metallic magnetic layer becomes equivalent to thespecific resistance value of the metallic magnetic layer of aconventional recording medium, even though the protection film may beformed at the similar speed, it is possible to acquire such a down-sizedor thinned-off recording medium. Conversely, in such a case in whichfilm thickness is identical to each other, the specific resistance valuedecreases and the speed of forming the protection film increases,whereby making it possible to manufacture recording media at a higherproduction rate.

Although the present invention has been described in its preferred formwith a certain degree of particularity, obviously many changes,combinations and variations are possible therein. It is therefore to beunderstood that the present invention may be practiced otherwise than asspecifically described herein without departing from the scope of thepresent invention.

1. A method of manufacturing a metallic thin film type magneticrecording medium comprising: arranging an initial substance of saidrecording medium in opposition to a plasma discharge electrode, saidinitial substance comprising a non-magnetic support base, a metalliclayer capable of functioning as a metallic electrode formed on saidnon-magnetic support base and a metallic magnetic layer formed on saidmetallic layer, and forming a protection film on a surface of saidinitial substance of said recording medium by way of generating plasmadischarge while feeding raw material gas between said metallic magneticlayer and said plasma discharge electrode.